食用油中植物甾醇氧化物风险评估、劣变机理及控制技术研究

发布时间：2018-08-27 08:26

【摘要】：植物甾醇(PS)具有显著降低人体血液中总胆固醇和低密度脂蛋白,抑制癌细胞增殖及消炎退热等功能,已被广泛应用于食品、制药、保健品等行业。在食品生产、储存、运输过程中,PS易受光、热、氧、金属离子等因素作用发生氧化劣变,生成具有健康危害作用的植物甾醇氧化物(POPs)。但是由于检测方法、模拟体系等因素的制约,目前国内外关于POPs的暴露风险、劣变机理和控制技术等方面的研究刚刚起步,有待深入探讨。本文以PS和POPs为研究对象,运用气相色谱-质谱联用(GC-MS)等检测手段结合数学建模和化学计量学方法,从POPs风险评估、劣变机理和控制技术三个方面进行系统研究,目的在于评估POPs的暴露风险,阐明PS劣变机理,探讨抗氧化剂抑制PS劣变的效果和作用位点。主要研究内容及结果总结如下:(1)建立并优化了一种食用油中34种POPs的GC-MS同步检测方法。方法学验证结果显示:在检测范围内,该方法线性关系良好,回归系数(R2)0.98,检出限低于36.30 ng/mL,日间精密度和日内精密度均小于10%,回收率89.72%～117.42%,并能应用于食用油及其他食品中各种低浓度POPs的检测。(2)基于Monte Carlo模拟评价了典型富油热加工食品(烘焙食品)中POPs的暴露和风险。暴露评估表明我国儿童、青少年、成人和老人等四大年龄组通过烘焙食品摄入POPs的平均暴露量分别为10.91、6.20、3.63和3.40 mg/(kg×day)。累积风险评估显示,在现有烘焙食品消费水平下,我国农村青少年、成人和老人群体的POPs中位暴露风险系数均小于1,暂无风险;城市各年龄段人群和农村儿童的风险系数处于1-10之间,处于风险范围,敏感性和不确定性分析显示,这种风险正在不断增加。(3)阐明了光照强度、加热温度、金属离子和脂质组成等4种因素对食用油中PS劣变的影响。光照强度与加热温度均与PS劣变呈现正相关,其劣变主要发生在B环C5、C6和C7位点上,形成以7-酮基、5α,6α/5β,6β-环氧、7α/β-羟基、6β-羟基和三羟基为主的氧化物。金属离子,特别是过渡态金属离子,在低浓度时即对PS劣变具有明显的促进作用。在高浓度金属离子作用下,PS除在B环上氧化生成常见POPs外,还会在A环上出现脱水烯化,生成甾烯化合物。不饱和脂质基质对PS劣变具有抑制作用,不饱和度越高,PS越不易劣变。(4)阐明了 PS化学结构与其热稳定性之间的关系。结果显示,各种PS的劣变规律均符合一级动力学模型,且模型回归系数良好,R20.9444。PS结构对稳定性影响主要体现在:双键数量越多,PS越易劣变;支链长度越长,PS越稳定;不同甾核的作用介于双键数量和支链长度之间;C7位点双键相比C5位点的更易劣变。进一步采用遗传算法(GA)结合偏最小二乘法(PLS)和主成分回归(PCR)构建QSAR模型,阐明PS拓扑结构与其热稳定性之间关系最密切。(5)探讨了 BHA、EGCG、VE和BHT等常见抗氧化剂对PS劣变的抑制效果和作用位点。研究发现4种常见抗氧化剂对PS劣变均具有一定抑制作用,其抑制效果从高到低依次为:BHAVEEGCGBHT,抑制率分别为22.8%、5.3%、3.5%和1.8%。对POPs生成抑制方面,BHT、EGCG和BHA使POPs生成速率分别下降7.80%、6.67%和6.53%,而VE反而促进9.51%的POPs生成。动力学研究结合劣变路径研究表明,4种抗氧化剂中BHA抑制效果最好,其主要抑制C5,C6位点的环氧化和C7位点转变为7-酮基甾醇的反应。综上所述,在目前烘焙食品消费水平下,经该途径摄入的POPs对于城市成人存在风险。食品加工过程中的光照强度、加热温度、金属离子的增加能促进PS劣变,不饱和脂肪酸酯、PS结构的饱和度和支链长度增加以及抗氧化剂的合理使用能抑制PS劣变。因此,在食品加工过程中,可以通过避免致变因素接触、添加抗氧化剂或者对PS进行结构改性等途径抑制PS劣变,达到防止PS营养流失,降低其产生健康风险的目的。
[Abstract]:Phytosterol (PS) has been widely used in food, pharmaceuticals, health products and other industries because of its remarkable functions of reducing total cholesterol and low density lipoprotein in human blood, inhibiting the proliferation of cancer cells, reducing inflammation and fever. Phytosterol oxides (POPs) are harmful to human health. However, due to the limitations of detection methods and simulation systems, the study on exposure risk, deterioration mechanism and control technology of POPs at home and abroad has just started, and needs to be further explored. In order to evaluate the exposure risk of POPs, clarify the mechanism of POPs deterioration, and explore the effect and action site of antioxidants to inhibit the deterioration of POPs, the risk assessment, deterioration mechanism and control technology of POPs were systematically studied with mathematical modeling and chemometrics methods. A GC-MS method for simultaneous determination of 34 POPs in edible oils was developed and optimized. The results of methodological validation showed that the method had good linearity, regression coefficient (R2) 0.98, detection limit less than 36.30 ng/mL, daytime precision and intraday precision less than 10%, recovery rate 89.72%-117.42%, and could be applied to edible oils and other oils. (2) Monte Carlo simulation was used to evaluate the exposure and risk of POPs in typical oil-rich hot-processed foods (baked foods). The exposure assessment showed that the average exposure of children, adolescents, adults and the elderly to POPs in baked foods was 10.91, 6.20, 3.63 and 3.40 mg / (kg) respectively. The cumulative risk assessment showed that the median exposure risk coefficients of POPs of rural adolescents, adults and the elderly were all less than 1 under the current level of baked food consumption, and there was no risk at present. The risk coefficients of urban and rural children of all ages were between 1 and 10, which were in the risk range. Sensitivity and uncertainty analysis showed that (3) The effects of light intensity, heating temperature, metal ions and lipid composition on the deterioration of PS in edible oils have been clarified. Both light intensity and heating temperature are positively correlated with the deterioration of PS. The deterioration mainly occurs at C5, C6 and C7 sites of B ring, resulting in the formation of 7-keto, 5a, 6a/5beta, 6beta-epoxy, 7a/beta-hydroxyl groups. 6-hydroxy and 3-hydroxy oxides. Metal ions, especially transition metal ions, can significantly promote the deterioration of PS at low concentrations. Under the action of high concentrations of metal ions, PS not only oxidizes to form POPs on B ring, but also dehydrates to form steroids on A ring. The results show that the deterioration laws of all kinds of PS conform to the first-order kinetic model, and the regression coefficients of the model are good. The influence of R20.9444. PS structure on the stability is mainly reflected in: the more the number of double bonds, the easier PS is. The longer the branched chains are, the more stable the PS is; the number of double bonds and the branched chains are between different steroid nuclei; the double bonds at C7 site are more likely to deteriorate than those at C5 site. Further, the QSAR model is constructed by genetic algorithm (GA), partial least squares (PLS) and principal component regression (PCR) to clarify the closest relationship between the topological structure of PS and its thermal stability. (5) Inhibitory effect and action site of BHA, EGCG, VE and BHT on PS deterioration were studied. The results showed that four kinds of common antioxidants had certain inhibitory effect on PS deterioration, and the inhibitory effect of BHAVEEGCGBHT was 22.8%, 5.3%, 3.5% and 1.8% respectively. HA decreased POPs production rates by 7.80%, 6.67% and 6.53% respectively, while VE increased POPs production by 9.51%. The increase of light intensity, heating temperature and metal ions during food processing can promote PS deterioration, unsaturated fatty acid esters, the increase of PS structure saturation and branched chain length, and the rational use of antioxidants can inhibit PS deterioration. In order to prevent nutrient loss and reduce health risk of PS, PS deterioration can be inhibited by avoiding contact with mutagenic factors, adding antioxidants or modifying PS structure.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TS221

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